Starch-hydrolyzed polyacrylonitrile graft copolymers exhibiting the capacity to absorb from about 300 to 1,000 times their weight of deionized water are known at this time. The development of these compositions was carried out by the Northern Regional Research Laboratory, Peoria, Illinois. The starch-hydrolyzed polyacrylonitrile graft copolymer is produced by exposure of starch, either gelatinized or ungelatinized, to cerium salt, such as cerium ammonium nitrate, which acts as a catalyst to generate free radicals. Acrylonitrile is then added. Polyacrylonitrile chains form at the site of these free radicals on the starch molecule. The resulting material is then saponified in sodium hydroxide to hydrolyze the polyacrylonitrile chains to carboxamide and alkali metal carboxylate groups mixed with metal salts. After drying, the material can absorb about 300 to 400 times its weight. Drying can be accomplished by drum, tumble air or vacuum drying. Extraction of the copolymer dispersion with alcohol before drying provides a material with fluid absorbency of 800 to 1,000 times its weight. The fluid absorbency is determined by suspending a weighed amount of dry copolymer in an excess of testing fluid and filtering to recover unabsorbed fluid.
The copolymer can be made as film, flakes, powder or mat. These forms take up water, swelling but not dissolving, and hold it in expanded duplications of their own dry shapes. Films extend and thicken to sheets. Powders become piles of water textured like crushed ice. A flake expands to a clear, angular piece of water. The swollen forms shrink in dilute acid and expand again in dilute alkali solution. They also shrink as they dry and expand again with water.
The copolymer, with these properties, can be mixed with or coated on a wide variety of materials including, for example, sand, straw, sawdust, seeds and roots, natural or synthetic fibers, and flour, gelatin and starch. It can hold water in soils, animal bedding and kitty litter, toweling and diapers, bandages, surgical pads and dental absorbents.
One disadvantage of the product is that when it is dispersed without vigorous agitation or without any agitation, the copolymer then wets on the outside of the particles and forms a layer which blocks further penetration of water. For example, when powdered copolymer is poured into a container holding water, the copolymer settles to the bottom forming gumballs or a block of material which is neither distributed nor dispersed in the media. In applications in which dry copolymer is used as an absorbent, this lack of wetting in a stationary position can completely negate the copolymer's usefulness. Stationary uses include absorbents for diapers, feminine hygiene napkins or tampons, bandages and the like.
Fatty quaternary ammonium chlorides are commercially available. These compounds are prepared by reacting a fatty amine with methyl chloride. Primary fatty amines yield the fatty trimethyl ammonium chlorides, secondary fatty amines produce difatty dimethyl ammonium chlorides and the tertiary fatty amines produce trifatty methyl ammonium chlorides. The structural formula for a fatty quaternary ammonium chloride is as follows: ##STR1## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are hydrogen or alkyl radicals with the proviso that there is at least one alkyl radical in the molecule.